<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <style type="text/css">
        * {
            padding: 0%;
            margin: 0%;
        }

        html,
        body {
            background: #f2f2f2;
        }

        .calendar {
            margin: 45px;
            width: 450px;
            height: 350px;
            background: white;
            box-shadow: 0px 1px 1px rgba(0, 0, 0, .1);
        }

        .title {
            height: 70px;
            border-bottom: 1px solid rgba(0, 0, 0, .1);
            position: relative;
            text-align: center;
        }

        #calendar-title {
            font-size: 25px;
            text-transform: uppercase;
            font-family: Arial, Helvetica, sans-serif;
            padding: 14px 0 0 0;
        }

        #calendar-year {
            font-size: 15px;
            font-family: Arial, Helvetica, sans-serif;
            font-weight: normal;
        }

        #pre {
            position: absolute;
            top: 0px;
            left: 0px;
            background: url(prev.png) no-repeat 50% 50%;

            /*没规定大小时，图片显示 0X0*/
            width: 60px;
            height: 70px;

        }

        #next {
            position: absolute;
            top: 0px;
            right: 0px;
            background: url(next.png) no-repeat 50% 50%;
            width: 60px;
            height: 70px;
        }

        .body-list ul {
            font-size: 14px;
            font-family: Arial, Helvetica, sans-serif;
            font-weight: bold;
            width: 100%;
            box-sizing: border-box;

        }

        .body-list ul li {
            list-style: none;
            /*
            display:inline-block; 
            width: 13.3%;
            */

            /*100/7 = 14.28%*/
            display: block;
            width: 14.28%;
            float: left;

            /*规定行高，垂直居中*/
            height: 36px;
            line-height: 36px;
            box-sizing: border-box;
            text-align: center;

        }


        .green {
            color: #6ac13c;
        }

        .lightgrey {
            /*浅灰色显示过去的日期*/
            color: #a8a8a8;
        }

        .darkgrey {
            /*深灰色显示将来的日期*/
            color: #565656;
        }

        /*日期当天用绿色背景绿色文字加以显示*/
        .greenbox {
            border: 1px solid #6ac13c;
            background: #e9f8df;
        }
    </style>
</head>

<body>
    <div class="calendar">
        <div class="title">
            <h1 class="green" id="calendar-title">Month</h1>
            <h2 class="green" id="calendar-year">Year</h2>
            <a href="" id="pre"></a>
            <a href="" id="next"></a>
        </div>

        <div class="body">
            <div class="lightgrey body-list">
                <ul>
                    <li>SUN</li>
                    <li>MON</li>
                    <li>TUE</li>
                    <li>WED</li>
                    <li>THU</li>
                    <li>FRI</li>
                    <li>SAT</li>

                </ul>

            </div>

            <div class="darkgrey body-list">
                <ul id="days">

                </ul>
            </div>
        </div>
    </div>

    <script type="text/javascript">
        var month_olypic = [31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31];//闰年每个月份的天数
        var month_normal = [31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31];
        var month_name = ["January", "Febrary", "March", "April", "May", "June", "July", "Auguest", "September", "October", "November", "December"];
        //获取以上各个部分的id
        var holder = document.getElementById("days");
        var prev = document.getElementById("prev");
        var next = document.getElementById("next");
        var ctitle = document.getElementById("calendar-title");
        var cyear = document.getElementById("calendar-year");
        //获取当天的年月日
        var my_date = new Date();
        var my_year = my_date.getFullYear();//获取年份
        var my_month = my_date.getMonth(); //获取月份，一月份的下标为0
        var my_day = my_date.getDate();//获取当前日期

        //根据年月获取当月第一天是周几
        function dayStart(month, year) {
            var tmpDate = new Date(year, month, 1);
            return (tmpDate.getDay());
        }
        //根据年份判断某月有多少天(11,2018),表示2018年12月
        function daysMonth(month, year) {
            var tmp1 = year % 4;
            var tmp2 = year % 100;
            var tmp3 = year % 400;

            if ((tmp1 == 0 && tmp2 != 0) || (tmp3 == 0)) {
                return (month_olypic[month]);//闰年
            } else {
                return (month_normal[month]);//非闰年
            }
        }
        //js实现str插入li+class,不要忘了用innerhtml进行插入
        function refreshDate() {
            var str = "";
            //计算当月的天数和每月第一天都是周几，day_month和day_year都从上面获得
            var totalDay = daysMonth(my_month, my_year);
            var firstDay = dayStart(my_month, my_year);
            //添加每个月的空白部分
            for (var i = 0; i < firstDay; i++) {
                str += "<li>" + "</li>";
            }

            //从一号开始添加知道totalDay，并为pre，next和当天添加样式
            var myclass;
            for (var i = 1; i <= totalDay; i++) {
                //三种情况年份小，年分相等月份小，年月相等，天数小
                //点击pre和next之后，my_month和my_year会发生变化，将其与现在的直接获取的再进行比较
                //i与my_day进行比较,pre和next变化时，my_day是不变的
                console.log(my_year + " " + my_month + " " + my_day);
                console.log(my_date.getFullYear() + " " + my_date.getMonth() + " " + my_date.getDay());
                if ((my_year < my_date.getFullYear()) || (my_year == my_date.getFullYear() && my_month < my_date.getMonth()) || (my_year == my_date.getFullYear() && my_month == my_date.getMonth() && i < my_day)) {
                    myclass = " class='lightgrey'";
                } else if (my_year == my_date.getFullYear() && my_month == my_date.getMonth() && i == my_day) {
                    myclass = "class = 'green greenbox'";
                } else {
                    myclass = "class = 'darkgrey'";
                }
                str += "<li " + myclass + ">" + i + "</li>";
            }
            holder.innerHTML = str;
            ctitle.innerHTML = month_name[my_month];
            cyear.innerHTML = my_year;
        }
        //调用refreshDate()函数，日历才会出现
        refreshDate();
        //实现onclick向前或向后移动
        pre.onclick = function (e) {
            e.preventDefault();
            my_month--;
            if (my_month < 0) {
                my_year--;
                my_month = 11; //即12月份
            }
            refreshDate();
        }

        next.onclick = function (e) {
            e.preventDefault();
            my_month++;
            if (my_month > 11) {
                my_month = 0;
                my_year++;
            }
            refreshDate();
        }
    </script>
</body>

</html>